Triangulation-based optical profilometry system

Abstract

A triangulation-based optical profilometry system for scanning a three-dimensional sample surface located at a sample plane includes a projection system; an image sensor; a processing unit; an objective lens assembly for imaging onto the image sensor a luminous line formed on the sample plane, a first direction orthogonal to an optical axis and being defined parallel to an extent of the luminous line, a second direction being defined perpendicular to the first direction; and a diaphragm defining a non-circular aperture defined by a first dimension and a second dimension greater than the first dimension, the diaphragm being rotationally oriented such that the first dimension is aligned with the first direction and the second dimension is aligned with the second direction, the objective lens assembly being arranged to form an out-of-focus image of the luminous line on the image sensor.

What is claimed is: 
     
       1. A triangulation-based optical profilometry system for scanning a three-dimensional sample surface located at a sample plane of the system, the system comprising:
 a projection system for projecting a luminous line across the sample surface, the luminous line extending laterally across the sample plane; 
 an image sensor for converting images of the luminous line, as projected on the sample plane, into electrical signals, the image sensor being a two-dimensional array of pixels; 
 a processing unit communicatively connected to the image sensor for processing the electrical signals; 
 an objective lens assembly for imaging the luminous line, as projected on the sample plane, onto the image sensor, the objective lens assembly defining an optical axis extending between the sample plane and the image sensor, 
 a lateral direction orthogonal to the optical axis and being defined parallel to an extent of the luminous line as projected, a vertical direction being defined perpendicular to the lateral direction, the lateral and vertical directions defining a plane orthogonal to the optical axis; and 
 a diaphragm disposed along the optical axis between the sample plane and the image sensor, the diaphragm defining a non-circular aperture therein, the aperture being defined by a first dimension and a second dimension perpendicular to the first dimension, the second dimension being greater than the first dimension, 
 the diaphragm being rotationally oriented relative to the image sensor such that the first dimension is aligned with the lateral direction and the second dimension is aligned with the vertical direction, 
 the objective lens assembly being arranged to form an out-of-focus image of the sample plane on the image sensor, 
 the diaphragm, the objective lens assembly, and the image sensor being arranged such that an image of a given point along the luminous line, as projected onto the sample surface and collected by the image sensor during operation of the system, exhibits greater vertical defocus than lateral defocus, 
 during operation of the system, the image of the given point of the luminous line extending over a greater number of pixels of the image sensor in the vertical direction than in the lateral direction. 
 
     
     
       2. The system of  claim 1 , wherein, during operation of the system, the image of the given point of the luminous line on the image sensor extends vertically over at least two pixels of the image sensor. 
     
     
       3. The system of  claim 1 , wherein the image sensor is disposed at a defocus position shifted along the optical axis away from an image plane of the sample plane as imaged by the objective lens assembly. 
     
     
       4. The system of  claim 1 , wherein the objective lens assembly includes a plurality of lenses. 
     
     
       5. The system of  claim 1 , wherein the diaphragm is disposed at an aperture stop of the objective lens assembly. 
     
     
       6. The system of  claim 1 , wherein the diaphragm is disposed at an entrance pupil of the objective lens assembly. 
     
     
       7. The system of  claim 1 , wherein the diaphragm is disposed at an exit pupil of the objective lens assembly. 
     
     
       8. The system of  claim 1 , wherein the second dimension of the aperture is about four times greater than the first dimension. 
     
     
       9. The system of  claim 1 , wherein a shape of the aperture is generally rectangular. 
     
     
       10. The system of  claim 1 , wherein a shape of the aperture is one of a geometric stadium, an oval, a rhombus, and a rounded-corner rectangle. 
     
     
       11. The system of  claim 1 , wherein the image sensor is one of:
 a charge-coupled device (CCD), 
 a complementary metal-oxide-semiconductor (CMOS) device, and 
 a N-type metal-oxide-semiconductor (NMOS) device. 
 
     
     
       12. The system of  claim 1 , wherein:
 a normal defined by the sample plane is skewed by a first angle (γ) relative to the optical axis; and 
 a normal defined by the image sensor is skewed by a second angle (γ′) relative to the optical axis. 
 
     
     
       13. The system of  claim 12 , wherein the first angle (γ) and the second angle (γ′) are arranged in a Scheimpflug configuration, such that the second angle (γ′) is chosen relative to the first angle (γ) according to the relation: 
       
         
           
             
               
                 
                   γ 
                   ′ 
                 
                 = 
                 
                   
                     tan 
                     
                       - 
                       1 
                     
                   
                   ⁡ 
                   
                     [ 
                     
                       
                         
                           S 
                           i 
                         
                         
                           S 
                           o 
                         
                       
                       ⁢ 
                       
                         tan 
                         ⁡ 
                         
                           ( 
                           γ 
                           ) 
                         
                       
                     
                     ] 
                   
                 
               
               , 
             
           
         
         where S i  is an image distance measured from the objective lens assembly to the image sensor and S o  is an object distance measured from the sample plane to the objective lens assembly. 
       
     
     
       14. The system of  claim 1 , wherein the projection system comprises:
 at least one illumination source; and 
 a projection optical assembly for projecting light from the illumination source onto the sample plane in the form of a line. 
 
     
     
       15. The system of  claim 14 , wherein:
 the at least one illumination source is a laser source; and 
 the luminous line is a laser line projected onto the sample plane.